viernes, 9 de junio de 2017

El fantasma de Canterville

No suelo incluir en este blog contenidos ajenos a mi materia de enseñanza pero hoy hago una excepción. Mis alumnos de 4ª ESO A han puesto en escena esta obra de teatro dentro de la asignatura de Inglés. La representación, que tuvo lugar en el Centro Joven de Badajoz, ha sido grabada por los alumnos del CF de imagen y sonido de nuestro instituto, el Rodríguez Moñino de Badajoz. Mi enhorabuena a los alumnos de 4º A y a su profesor Carlos Criado por el esfuerzo invertido y el resultado obtenido.

Physics and TV: Cosmos, a spacetime odissey.

Cosmos: A Spacetime Odyssey is probably the best science documentary TV series ever. This series deals with fascinating topics such as the universe, the history of science and the evolution of life. The series, produced by Neil DeGrasse Tyson is a remake of the one produced by Carl Sagan in 1979. The new version not only improves the digital effects of the original one but also updates its scientific contents. Cosmos: A Spacetime Odyssey is an absolute "must" for all those that like science. The series deals with science stuff in a very accurate and spectacular way.

Here you have the official trailer:

jueves, 8 de junio de 2017

Caída libre en la Luna y en un tubo de vacío

Como podemos ver en estos vídeos, el movimiento de caída libre de los cuerpos no depende de su masa.
Caída libre en la Luna donde, como sabes, no hay atmósfera.

Caída libre dentro de un tubo de vacío

Caída libre en la cámara de vacío mas grande del mundo

miércoles, 7 de junio de 2017

martes, 6 de junio de 2017

lunes, 5 de junio de 2017

viernes, 19 de mayo de 2017

Physics and TV: Genius

A highly recommendable TV series for those who like physics is Genius. This show is on the screen on National Geographic Channel, available on some cable and satellite TV providers. The series tells us the life and work of one of the most brilliant scientists ever: Albert Einstein. It shows us not only the scientist and his crucial works but also his personal life and how the rise of nazism in Germany affected to the most famous Jew of the 20th century. Not only it is a very entertaining program but it is also very educational. It provides a quite comprehensible approach to his paramount contributions, such as his proofs of the existence of molecules, his explanations for the photoelectric effect or the most revolutionary physics ideas ever: the theory of relativity. An absolute "must" for those who like science or TV series.

viernes, 12 de mayo de 2017

Physics and movies: Up

I don't know anyone who dislikes Disney-Pixar's UP. This story of friendship between an elderly man and a boy is very inspiring. The movie deal with a physics principle: buoyancy. The movie tells us how a recently widower man tries to make his wife's dream real by traveling to South America. To do so, he uses his house as a mean of transport by making it float in the air. According to the plot, the house goes up thanks to the buoyancy force produced by thousands of helium balloons. Would that work? A National Geographic TV show tried to recreate the set-off of the house and got the result you can see in the video below.


Despite it is a lightweight house specially designed for this experiment, a lot of helium was used. Could something like that be done with an actual house like the ones that people live in? How much helium would be needed? According to an estimation by, a 150-squared-meter house may have a mass of roughly 100 tons. Are you able to estimate the volume of helium that could make a house fly?

Let's do the math.

First, we can get some info from the video. They use 300 balloons. Each of them has a diametre of 8 ft (2.44 m). The reporter says that it was almost freezing, so I will assume they are at STP conditions. We also need additional data, such as helium and air densities:
He: 0.179 kg/m3
Air: 1.295 kg/m3.

How much helium do they use?
Each balloon is a sphere with a radius of 1,22 m. Its volume can be easily calculated: 7.59 m3. All the balloons together add up a volume of 2277 m3. Multiplying by its density we figure out that the mass of helium inside the balloon is 407.5 kg which has a weight of 3994 N.

What buoyancy force can be obtained from that mass of Helium?
The buoyancy force is the weight of the fluid displaced by the balloon. In this case we have to calculate the weight of 2277 m3 of air.
E = 1.295 kg/m3 · 2277 m3 · 9.8 m/s2 = 28897N.

This buoyancy force has to be strong enough to rise not only the house but also the helium itself. The weight of cannot be greater than 28897 N - 3994 = 24903 N, so it has to be lighter than 2541 kg, roughly two and a half tons. To rise an actual house, like the one you may live in, with an estimated mass of 100 tons we would need forty times more Helium, which is 91080 m3. That volume is the equivalent of a sphere with a radius of 28 m. Take the volume of a party balloon (0,91 according to the website a party stuff provider company) into account we conclude that 100000 balloons would be needed. I honestly was expecting an even higher number of balloons. In fact, we would need much more balloons, at least to set the house off. Don't forget the force we have just calculated is the one required to lift the house but, to set off we have to pull it out from its foundations and higher buoyancy force would be required.